Optical sheet and method of manufacturing the same

ABSTRACT

An optical sheet includes a light-passing base sheet, a plurality of light-passing first patterns formed on a front major surface of the base sheet, and a plurality of light-passing second patterns formed on a rear major surface of the base sheet. The first patterns protrude from the front surface of the base sheet, a top portion of each of the second patterns makes contact with the rear surface of the second patterns while a larger lower surface of each of the second patterns is exposed to serve as a light receiving surface. Voids having relatively low refractive indices are formed between the light-passing second patterns. The optical sheet employs just one base sheet in one embodiment, thereby reducing a manufacturing cost of the optical sheet.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 13/180,283 filed on Jul. 11, 2011, which claimspriority to Korean Patent Application No. 10-2010-0115818 filed on Nov.19, 2010; where the disclosures of both said applications areincorporated herein by reference in their entirety.

BACKGROUND

1. Field of Disclosure

The present disclosure of invention relates to an optical sheet for usein a backlit liquid crystal display and a method of manufacturing theoptical sheet.

2. Description of Related Technology

In general, a liquid crystal display (LCD) displays an image usingchange in optical transmittance attributes (e.g., polarization) ofliquid crystals according to correspondingly applied voltages. To thisend, the liquid crystal display typically includes a backlight unit anda liquid crystal display panel.

The backlight unit provides light to a back or rear portion of theliquid crystal display panel. A user of the LCD apparatus views a formedimage by facing a front portion of the LCD panel. The backlight unitgenerally includes a light source that can emit white and/or other lightand optical sheets that control an optical path and shape of thebacklight output light to improve brightness and uniformity of the lightbefore it is provided to the liquid crystal display panel.

For liquid crystal displays in recent times, it is desired to havefeatures like greater slimness and lower power consumption and todevelop backlight units having lower manufacturing costs and higherbrightness levels so as to be cost competitive and feature competitive.

It is to be understood that this background of the related technologysection is intended to provide useful background for understanding thehere disclosed technology and as such, the technology background sectionmay include ideas, concepts or recognitions that were not part of whatwas known or appreciated by those skilled in the pertinent art prior tocorresponding invention dates of subject matter disclosed herein.

SUMMARY

One way to reduce power consumption is to increase the efficiency oflight transference as such occurs for example between the backlightingsource and a prismatic portion of the backlight optics section. Morespecifically, in conventional prismatic films of plates, the underneathportion has prismatic structures with downwardly pointing apexes.Incident light that strikes the sloped surfaces of these conventionalunderneath prismatic structures is partially reflected at theair-to-polymer interface. However, in accordance with one aspect of thepresent disclosure, the air-to-polymer interface is inverted so thatincident light from underneath does not directly strike it whenincoming, but rather exits from that inverted air-to-polymer interface(where the inverted air-to-polymer interface could be called apolymer-to-air interface, or P2A-IF for short). As a result, reflectionlosses are reduced and efficiency of light transference is improved,thus enabling reduced power consumption. Additionally, the thickness ofthe prismatic portion of the backlight optics section can be reducedwhen the polymer-to-air interface (P2A-IF) configuration is used.

Exemplary embodiments of the present disclosure additionally, provide aprismatic optical sheet that is capable of reducing manufacturing costand improving reliability.

Exemplary embodiments of the present disclosure include a method ofmanufacturing the optical sheet.

According to an exemplary embodiment, an optical processing sheetincludes a light-passing base sheet formed of a first material having arespective relatively high refractive index. A plurality oflight-passing first patterns are provided protruding from an upper,front surface of the base sheet, and a plurality of light-passing secondpatterns are provided as attached to a lower, rear surface of the basesheet. The first and second patterns are formed of respective materialshaving respective relatively high refractive indices. Voids are createdbetween the second pattern to thus create a lightpasser-to-air interface(LP2A-IF) configuration which reduces back reflection of incoming lightthat comes into the bottoms of the second patterns for processingthereby. In one embodiment, the second patterns provide a lightconverging function in a first set of parallel planes each extending ina first direction (D1).

In one embodiment, the first patterns protrude from the front surface ofthe base sheet and have a prism mountain shape extending longitudinallyin the first direction so as to provide a light converging function in asecond set of parallel planes each extending in a second direction (D2)different from the first direction (D1). The second direction may beperpendicular to the first direction.

Lower base vertices of the second patterns are connected one to the nextfor example with a flexible and light-passing adhesive. Each of thesecond patterns has a trapezoidal prismatic shape in one embodiment thatextends longitudinally in the second direction. The optical sheet mayfurther include a protective layer disposed on the lower surface of thesecond patterns to prevent the second patterns from being easilyseparated.

According to an exemplary method of manufacture, the optical processingsheet is provided as follows. A plurality of second patterns arereleasably adhered to a top surface of an auxiliary base sheet or platesuch that the second patterns protrude upwardly therefrom, and aplurality of first patterns are formed on an upper, front surface of abase sheet to allow the first patterns to protrude upwardly therefrom.Then, an adhesive layer is formed on a rear surface of the base sheet,and the structure on top of the auxiliary base sheet is coupled with thebase sheet such that the second patterns make contact with the adhesivelayer. After that, the auxiliary base sheet is releasably removed toexpose a lower surface of the second patterns.

Other aspects of the present teachings will become apparent from thebelow detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the present teachings will becomereadily apparent by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is an exploded perspective view showing a display apparatus withan optical sheet structured according to an exemplary first embodimentof the present disclosure;

FIG. 2 is a perspective view showing an optical sheet according to thefirst exemplary embodiment wherein a lower prismatic portion includes apolymer-to-air interface (P2A-IF) configuration rather than anair-to-polymer interface configuration;

FIG. 3 is a cross-sectional view taken along a line III-III′ of FIG. 2;

FIG. 4 is a perspective view showing an optical sheet according to asecond exemplary embodiment;

FIG. 5 is a cross-sectional view taken along a line IV-IV′ of FIG. 4;

FIG. 6 is a perspective view showing an optical sheet according to athird exemplary embodiment;

FIG. 7 is a cross-sectional view showing an optical sheet according to afourth exemplary embodiment;

FIG. 8 is a perspective view showing an optical sheet according to afifth exemplary embodiment;

FIG. 9 is a cross-sectional view showing an optical sheet according to asixth exemplary embodiment;

FIG. 10 is a cross-sectional view showing an optical sheet according toa seventh exemplary embodiment;

FIG. 11 is a perspective view showing an optical sheet according to aneighth exemplary embodiment;

FIG. 12 is a perspective view showing an optical sheet according to aninth exemplary embodiment;

FIGS. 13A to 13E are views showing a method of manufacturing an opticalsheet according to the first exemplary embodiment; and

FIGS. 14A to 14E are views showing a method of manufacturing an opticalsheet according to the second exemplary embodiment.

DETAILED DESCRIPTION

It will be understood that when an element or layer is referred to asbeing “on”, “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. Like numbers refer to likeelements throughout. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that although the terms first, second, etc. may beused herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother region, layer or section. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the present disclosure.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms, “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “includes”and/or “including”, when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Hereinafter, the present disclosure of invention will be explained indetail with reference to the accompanying drawings.

FIG. 1 is an exploded perspective view showing a display apparatus witha prismatic optical sheet structured and disposed according to anexemplary first embodiment of the present disclosure.

Referring to FIG. 1, a display apparatus 100 includes an upper cover orhousing piece 110, a lower cover or housing piece 190, a display panel120, a mold frame 130 disposed and structured to support the displaypanel 120, and a backlight unit disposed and structured to provide whiteand/or other light to the display panel 120. The display panel 120, themold frame 130, and the backlight unit are disposed between the uppercover 110 and the lower cover 190.

The upper cover 110 covers a front surface of the display panel 120 andthus protectively houses a corresponding front part of the display panel120. The upper cover 110 is provided with a window 111 to expose adisplay area of the display panel 120. The upper cover 110 may beprovided with a fastening or coupling mechanism such as a screw hole(not shown) at a side surface thereof for securing the upper cover 110to another portion of the assembly 100. The lower cover 190 is disposedand structured to receive and house at least a rear portion of thedisplay panel 120 and to receive and house the backlight unit.

The display panel 120 displays an image toward a front side thereof. Inthe present exemplary embodiment shown in FIG. 1, the display panel 120is a liquid crystal display (LCD) panel, but it should not be limitedthereto or thereby and other types of flat panel displays (e.g.,electrophoretic) which may use prismatic optical sheets are understoodto be within the contemplation of the disclosure.

The display panel 120 includes a first substrate 121, a second substrate122 facing the first substrate 121, and a liquid crystal layer (notshown) disposed between the first substrate 121 and the second substrate122. The first substrate 121 includes a plurality of pixel electrodesand the second substrate 122 includes a common electrode. The displaypanel 120 includes or is operatively coupled to a circuit (not shown)that selectively applies respective voltages to respective one of thepixel electrodes so as to thus create electric fields extending to thecommon electrode and the arrangement or alignment of liquid crystalmolecules in the liquid crystal layer is thus controlled by the electricfields formed between the pixel electrodes and the common electrode,thereby displaying a desired image toward the front side of the assembly100. The first substrate 121 may further include a plurality of thinfilm transistors each coupled to a respective pixel-electrode and thesecond substrate 122 may further include a plurality of color filterssuch as Red, Green and Blue color filters disposed above respective onesof the pixel-electrodes.

The mold frame 130 is disposed under the display panel 120 to supportthe display panel 120. The mold frame 130 has a rectangular annularshape which corresponds with non-displaying peripheral edge areas of thedisplay panel 120.

The backlight unit is disposed below the mold frame 130 to provide lightthrough the mold frame 130 to the display area of the display panel 120.The illustrated backlight unit includes a plurality of discrete lightsources 170, a reflective sheet 180, an optical sheet 150, a diffusionsheet 160, and a protective sheet 140.

The light sources 170 each emit respective white or other light. In FIG.1, the light sources 170 are disposed over substantially an entire rearsurface area of the display panel 120, but they should not be limitedthereto. That is, the light sources 170 may be alternatively oradditionally positioned at the outermost edges of the rear surface areaof the display panel 120 so as to provide so-called, edge lighting. Inone embodiment, light emitting diodes (LED's) are used as the lightsources 170, but the light sources 170 may include cold cathodefluorescent lamps, external electrode fluorescent lamps, or hot cathodefluorescent lamps.

The reflective sheet 180 is disposed under the light sources 170 toreflect light that has not been directly projected toward the front partof the display panel 120 such that the reflected light travels towardthe front part of the display panel 120.

The diffusion sheet 160 is disposed above the light sources 170 todiffuse the light from the discrete light sources 170 and thus reducethe discrete nature of that light by making it more homogenous. In oneembodiment, the diffusion sheet 160 has substantially flat upper andlower major surfaces and light diffusing agents embedded within itsbody. More specifically, at least the upper major surface issubstantially flat so as to enable a correspondingly flat, lower majorsurface of the optical sheet 150 to mate there with without having anair pocket interposed between the diffusion sheet 160 and the overlyingoptical sheet 150.

The optical sheet 150 is disposed above the diffusion sheet 160(optionally makes direct contact with the diffusion sheet 160) and it isstructured to receive the diffused light rays output by the diffusionsheet 160 and to project the received rays upwardly in a directionsubstantially perpendicular to the front and rear major surfaces of thedisplay panel 120. Details of the optical sheet 150 will be describedlater.

The protective sheet 140 is disposed on the optical sheet 150 to protectthe optical sheet 150 from scratching, chemical corrosion and/or thelike. In the present exemplary embodiment, the protective sheet 140 maybe omitted from the backlight unit, and the backlight unit may furtherinclude a polarizing film or a brightness enhancing film in addition toor instead of the protective sheet 140.

FIG. 2 is a perspective view showing an optical sheet according to afirst exemplary embodiment of the present disclosure, and FIG. 3 is across-sectional view taken along a line III-III′ of FIG. 2.

Referring to FIGS. 2 and 3, the optical sheet 150 includes alight-passing base sheet 153 having front and rear major surfacesrespectively denoted as 153F and 153R. The optical sheet 150 furtherincludes a plurality of first patterns 154 disposed on the front surface153F of the base sheet, and a plurality of second patterns 152 disposedon the rear surface 153R of the base sheet. In one embodiment, each ofthe base sheet 153, the first patterns 154 and the second patterns 152is respectively composed of a respective light-passing material havingan index of refraction (n_(j)) greater than that of air.

The base sheet 153 has a rectangular plate shape when viewed from thefront. The base sheet 153 may be formed of a light-passing material suchas one that is formed from polymer resin such as polyethyleneterephthalate (PET) and the base sheet 153 may have a thickness of about125 micrometers to about 250 micrometers.

The first patterns 154 (e.g., triangle-ended prisms) are disposed on andmake contact with and substantially cover the front surface 153F of thebase sheet. The first patterns 154 protrude upwardly along a normal linedirection of the front surface 153F. Each of the first patterns 154extends longitudinally in a first direction D1 and has a substantiallytriangular or mountainous shape when viewed in the cross sectioningplane of second direction D2. In one embodiment, the mountain shapedfirst patterns 154 are disposed one after the next along the frontsurface 153F of the base sheet to have a pitch dimension (P1) of about50 micrometers to about 100 micrometers. The first patterns 154 may beformed of an acrylic-based polymer resin, and each mountain shape mayhave a height of about 25 micrometers to about 30 micrometers

The first patterns 154 may optically operate in a manner similar toconvex lenses and may thus refract light that is incident to their rearor base portions (154R) as upwardly more focused or more collected lightthat is aimed at the LCD panel above them. Since the first patterns 154extend longitudinally in the first direction D1, the light is caused tobe more collected or more converged in the plane of the second directionD2, where the latter is perpendicular to the first direction D1.

The second patterns 152 are disposed on the rear surface 153R of thebase sheet 153. However unlike the first patterns 154, the secondpatterns 152 do not make essentially direct contact with substantiallythe entire surface area of the rear surface 153R and instead the secondpatterns 152 are shaped to create air pockets 159 (or more broadlyspeaking, regions of relatively low refractive index) near the rearsurface 153R of the base sheet. On the other hand, the collectiveunderneath surface (all the 152B's combined) presents a substantiallycontinuous flat and light receiving surface of relatively highrefractive index to incoming light rays arriving thereto, for example,from the diffusion sheet 160. This configuration allows for improvedefficiency of transference of light energy (e.g., reduced backreflection) from the diffusion sheet 160 to the optical sheet 150 asshall become clearer from the more detailed description below.

Each of the second patterns 152 extends longitudinally in the seconddirection D2 as a prism having substantially trapezoidal ends orfrusto-mountain shapes. In other words, and as shown in FIGS. 2 and 3, atop portion of each of the second patterns 152 is cut flat, so that eachof the second patterns 152 has an upper surface 152T of lateraldimension smaller than the bottom portion or base 152B of thetrapezoidal shape. The flat topped, small upper surfaces 152T of thesecond patterns 152 run substantially parallel to the rear surface 153Rof the base sheet so as to thereby allow the second patterns 152 toalmost contiguously couple with the material of the base sheet 153.Stated otherwise, each of the second patterns 152 has a trapezoid shapeat its cross sectional view when seen in a plane extending in the firstdirection D1. The second patterns 152 may be formed of a light-passingmaterial of refractive index greater than air such as of anacrylic-based polymer resin. When the second patterns 152 are attachedto the of the base sheet 153, as will be described, a separate andadditional base sheet is not required to support the lower portions(152B) of the second patterns 152 in the finished LCD apparatus 100 andthus the thickness of the LCD apparatus 100 is not increased byinclusion of such an additional base sheet (not shown). Instead, thelower surfaces 152B of the second patterns 152 are exposed so that theycan make direct contact with the next lower portion of the finished LCDapparatus 100 (e.g., the diffusion sheet 160), where this direct contactwith the next lower portion (e.g., 160) can occur without making contactwith air or another medium of relatively low refractive index and thusback reflection of incoming light (light coming up from the yet lowerbacklight sources 170) can be reduced and energy coupling can beimproved.

The upper surface 152T of each of the second patterns 152 makes directcontact with a corresponding portion of the rear surface 153R of thebase sheet. The lower surfaces 152B of adjacent ones of the secondpatterns 152 are essentially or substantially connected to each other sothat air pockets 159 of substantially prismatic form with triangle endsare formed under portions of the rear surface 153R which are notcontacted by the upper surfaces 152T of the second patterns 152. Asmentioned above, this formation of the prismatic air pockets 159 abovethe collective surface area of the bottom surfaces (combined 152B's) ofthe second patterns 152 may be referred to as a polymer-to-air interface(P2A-IF) configuration. In the present exemplary embodiment, the widthdimension of the lower surface 152B in the first direction D1 of eachsecond pattern 152 is greater than the width dimension of the uppersurface 152T thereof in the first direction D1.

The width of the lower surface 152B (which corresponds with air pocketpitch P2) may be about 50 micrometers to about 100 micrometers in thefirst direction D1. In one embodiment, the pitch P2 of the formed,prismatic air pockets 159 is made to be larger than the pitch P1 (FIG.2) of each of the overlying first patterns 154. This difference inpitches (P2>P1) can operate to improve the light-collecting (lightun-diffusing) efficiency. In addition, each of the second patterns 152may have a height H1 of about 25 micrometers to about 30 micrometerssimilar to that of the first patterns 154.

The substantially trapezoidal second patterns 152, because they aresurrounded by air pockets 159, can operate as convex lens that collect(un-diffuse) the light rays incident thereto from underneath so that thelight rays converge more when traveling towards the front of the LCDpanel (in a D3 direction, not shown). Since the prismaticfrusto-mountain shape of each of the second patterns 152 appears inplanes extending in the first direction D1, the light is collected orconverged in such planes of the first direction D1.

As described above, the light emitted from the light sources 170 is morecollected (more converged) in the first and second directions D1 and D2after passing through the second patterns 152 and the first patterns154, and thus most of the pre-diffused light that is provided from theunderlying diffusion sheet 160 to the optical sheet 150 may be furtherrelayed, with little loss due to back reflection to the overlyingdisplay panel 120. As a result of this improved transfer of lightenergy, the light sources 170 may be operated at lower power levels andpower consumption may be reduced, thereby enabling longer battery lifein portable devices (e.g., laptop computers) that employ the heredisclosed optical sheet 150.

In one embodiment, an adhesive layer 157 is pre-coated on the rearsurface 153R of the base sheet 153 to assist in attaching the topsurfaces 152T of the second patterns 152 to the base sheet 153. Thesecond patterns 152 are pressed substantially through the adhesivecoating (157) so that, as shown in FIG. 3, the adhesive coating issubstantially pushed aside to form thickened areas of adhesive adjacentto sides of the top surfaces 152T and the subsequently hardened adhesivelayer 157 thus surrounds the upper portions of the second patterns 152and thus affixes the second patterns 152 to the lower surface 153R ofthe base sheet 153.

At its thickest parts, the hardened adhesive layer 157 may have athickness of about 0.1 micrometers to about 5 micrometers and it may beformed of a relatively high refractive index material such as at leastone of an acrylic-based polymer resin, a polyester-based polymer resin,or a polycarbonate-based polymer resin. The adhesive layer 157 may havedistributed therein at least one light diffusing agent such as anorganic diffusing agent or inorganic diffusing agent to diffuse thelight passing through the thick parts of the adhesive layer 157. Thus,even though the air pockets 159 may be viewed as operating like concaverather than convex lenses (due to their relatively low refractiveindex), the embedded light diffusing agent(s) in the thick parts of theadhesive layer 157 soften the undesired optical effects (light divergingrather than light converging) of the air pockets 159. Although not shownin the figures, it is to be understood that a very thin portion of theadhesive layer 157 may remain between the rear surface 153R of the basesheet 153 and the upper surface 152T of the second patterns 152 afterpress attachment, thereby enhancing adhesive force between the basesheet 153 and the second patterns 152.

As mentioned, an air layer 159 is created between the second patterns152 but above the collective light receiving surface formed by the closetogether or touching or flexibly joined (by trace amounts of adhesive)lower surfaces 152B of the second patterns 152. According to Snell'slaw, a bending angle of light becomes larger as a difference ofrefractive indices between two interface mediums becomes larger. Sincethe air in pockets 159 has a relatively low refractive index (about 1.0)as compared with that (>1) of the other materials mentioned here, thelight-collecting efficiency of the optical sheet 150 may be improved dueto difference in refractive indices as between the material of thesecond patterns 152 and the interfacing air layer 159. (It is alsowithin the contemplation of the present disclosure to fill the airpockets 159 with a light-passing material that has a relatively lowrefractive index. However such may disadvantageously operate to increasecosts and reduce the light converging efficiency of the optical sheet150.) The air layer 159 has a height H2 smaller than the height H1 ofthe second patterns 152 and corresponding to a difference between theheight of the thick portions of the adhesive layer 157 and the height H1of the second patterns as shown in FIG. 3. That is, since the adhesivelayer 157 has the height of about 0.1 micrometers to about 5 micrometersin its thickest portions, the height H2 of the air layer 159 correspondsto a value of about 0.75 times (i.e., 75%) the height H1 of the secondpatterns 152 in one embodiment.

The optical sheet 150 having the-above described stricture may have thelight-collecting efficiency higher than that of a conventional prismsheet where the conventional air-to-polymer interface configuration (notshown) is used. (Although not directly illustrated, the so-called,conventional air-to-polymer interface configuration may be imagined bytaking a copy of first patterns 154 as shown in FIG. 2, collectivelyflipping them upside down and substituting that flipped copy in place ofillustrated second patterns 152 of FIG. 2.) In addition, the opticalsheet 150 includes the first patterns 154 and the second patterns 152that are extending in the direction perpendicular to the first patterns154, so that the optical sheet 150 may collect (converge) the light inthe planes of both axes as the light travels from the rear (152B) to thefront side of the optical sheet 150. In addition, since the air layerhaving the relatively high refractive index is formed between the secondpatterns 152, the light-collecting efficiency for the light passingthrough the optical sheet 150 may be improved.

In addition, the optical sheet 150 employs just one base sheet 153 forholding the assemblage together, and thus the manufacturing cost for theoptical sheet 150 may be reduced. According to the structure of theoptical sheet 150, the base sheet 153 may be prevented from being curledor wrinkled due to a difference of heat expansion coefficients betweenthe layers on which the first and second patterns 154 and 152 are formedand the layer of the base sheet 153 because, for example, they are madeof same or similar polymer materials. As a result, the optical sheet 150may have improved reliability.

FIG. 4 is a perspective view showing an optical sheet according to asecond exemplary embodiment, and FIG. 5 is a cross-sectional view takenalong a line IV-IV′ of FIG. 4. In FIGS. 4 and 5, the same referencenumerals denote the same elements in FIGS. 1 to 3, and thus detaileddescription of the same elements will be omitted.

Referring to FIGS. 4 and 5, an optical sheet 250 includes a base sheet153, a plurality of first patterns 154, a plurality of second patterns152, and a protective layer 155. The protective layer 155 is formedsubstantially over the entire collective lower surface (152B's) of thesecond patterns 152 so as to substantially entirely cover and protectthe lower surface of the second patterns 152. The protective layer 155may interface with the underlying diffusion sheet 160.

As shown in FIGS. 4 and 5, the second patterns 152 are not onlyconnected to each other by only the adhesive 157 at the upper surfaces152T thereof but also by means of the protective layer 155. That is, ifconnection is provided only by the adhesive 157, the second patterns 152may easily become separated one by one from the base sheet 153 whenexternal impacts are applied to the second patterns 152. However, asshown in FIGS. 4 and 5, when the protective layer 155 is formed on andadhered to the lower surfaces 152B of the second patterns 152, thesecond patterns 152 may be prevented from being separated from the basesheet 153.

The protective layer 155 may include an acrylic-based polymer resin or apolyurethane-based polymer resin. In addition, the protective layer 155may include the same material as the second patterns 152 and may beintegrally formed with the second patterns 152. In one embodiment, theprotective layer 155 is formed of a material different from that of thebase sheet 153.

In order to sufficiently support the second patterns 152, the protectivelayer 155 has a thickness H3 of about 5 micrometers or more, whichcorresponds to a value of 0.25 times (25%) or more the height H1 of thesecond patterns 152. For instance, in the case that each of the secondpatterns 152 has the height H1 of about 25 micrometers to about 30micrometers, the protective layer 155 may have the thickness H3 of about5 micrometers to about 10 micrometers. As the thickness H3 of theprotective layer 155 becomes thicker, the separation of the secondpatterns 152 may be more effectively prevented. However, it ispreferable that the thickness H3 of the protective layer 155 is smallerthan the height H1 of the second patterns 152 in consideration ofprocess conditions and also because this helps to reduce the overallthickness of the optical sheet 250.

The optical sheet 250 according to the second exemplary embodiment isobtained by adding the protective layer 155 to the optical sheet 150according to the first exemplary embodiment. Accordingly, the opticalsheet 250 may prevent the base sheet 153 from being curled or wrinkledand reduce the manufacturing cost thereof. In addition, since theoptical sheet 250 may prevent the second patterns 152 from beingseparated by using the protective layer 155, adhesive force between thesecond patterns 152 may be enhanced.

In the first and second exemplary embodiments, the first patterns 154and the second patterns 152 have been schematically represented ashaving the shape of the prism mountain, but they should not be limitedthereto or thereby. Any appropriate shape for providing the desiredlight convergence function may be used, for example half cylinders asare shown in FIG. 6.

Referring to the specifics of FIG. 6, this is a perspective view showingan optical sheet 350 according to a third exemplary embodiment. FIG. 7is a cross-sectional view showing an optical sheet 450 according to yeta fourth exemplary embodiment.

In FIG. 6, the optical sheet 350 includes first patterns 354, eachhaving a lenticular shape (e.g., half cylindrical). The first patterns354 have the light-collecting efficiency different from that of thefirst patterns 154 in the first exemplary embodiment. In addition,although not shown in FIG. 6, the first patterns 254 may have variousshapes, such as a half-circular shape, a half-oval shape, a hybridpyramid-rounded apex shape, etc., instead of the lenticular shape.

Referring to FIG. 7, an optical sheet 450 includes second patterns 452,each having a lenticular shape of which an upper surface is parallel tothe base sheet 153 by cutting away the upper portion of the secondpatterns 252. Similar to the third exemplary embodiment, the secondpatterns 452 may have various shapes, such as a half-circular shape ofwhich the upper portion is cut away, a half-oval shape of which theupper portion is cut away, a pyramid shape of which the upper portion iscut away, instead of the lenticular shape of which the upper portion iscut away.

As described above, the first and second patterns may have variousshapes, thereby variously controlling the light-collecting efficiency.In addition, the base sheet 153 may be prevented from being curled orwrinkled due to a heat expansion coefficient difference between layerson which the first and second patterns 354 and 452 are formed and thelayer of the base sheet 153. As a result, the optical sheet 350/450 mayhave improved reliability.

FIG. 8 is a perspective view showing an optical sheet 550 according to afifth exemplary embodiment.

Referring to FIG. 8, an optical sheet 550 includes a base sheet 153, aplurality of first patterns 154, a plurality of second patterns 152, anda protective layer. The protective layer (150-1, 150-2, . . . , 150-N)is disposed below the second patterns 152. The protective layer includesa plurality of rib or bar like supporters 155-1 and 155-2 that areextended longitudinally in the first direction D1 and arranged in spacedapart fashion along the second direction D2.

The supporters 155-1, 150-2, . . . , 150-N may be formed of alight-passing material that is formed from an acrylic-based polymerresin or a polyurethane-based polymer resin. The supporters 155-1,155-2, etc. may include the same material as used for the secondpatterns 152 and may be monolithically integrally formed with the secondpatterns 152.

In FIG. 8, the supporters 155-1, 155-2, etc. are spaced apart from eachother while being disposed below the second patterns 152, but theyshould not be limited thereto or thereby. That is, the supporters may bedisposed only on a side surface of the optical sheet 550.

In order to sufficiently support the second patterns 152, the supporters155-1, 155-2, etc. 2 have a thickness of about 5 micrometers or more,which corresponds to a value of 0.25 times (25%) or more the height ofthe second patterns 152. For instance, in the case that each of thesecond patterns 152 has the height of about 25 micrometers to about 30micrometers, the supporters 155-1, 155-2, etc. may have the thickness ofabout 5 micrometers to about 10 micrometers. As the thickness of thesupporters 155-1, 155-2, etc. becomes thicker, the separation of thesecond patterns 152 may be more effectively prevented. However, it ispreferable that the thickness of the supporters 155-1, 155-2, etc. issmaller than the height of the second patterns 152 in consideration ofprocess conditions.

In addition, the optical sheet 550 employs one base sheet 153 to collectthe light, and thus the manufacturing cost for the optical sheet 150 maybe reduced. The optical sheet 550 may prevent the base sheet 153 frombeing curled or wrinkled. In addition, since the optical sheet 550 mayprevent the second patterns 152 from being separated by using thesupporters 155-1 and 155-2, adhesive force between the second patterns152 may be enhanced.

FIG. 9 is a cross-sectional view showing an optical sheet according to asixth exemplary embodiment.

Referring to FIG. 9, an optical sheet 650 includes a base sheet 153, aplurality of first patterns 154, a plurality of second patterns 152, anda second adhesive layer 156. The second adhesive layer 156 is disposedbetween the second patterns 152 to connect ends of two adjacent secondpattern bottoms 152B. In detail, each of the second patterns 152 has theshape of the prism mountain, and the second adhesive layer 156 covers anarea at which a base vertex of a first prism mountain meets a basevertex of an adjacent second prism mountain, thereby preventing thesecond patterns 152 from being easily separated from each other.

The second adhesive layer 156 may include the same material as theadhesive layer 157 that fixes the second patterns 152 to the base sheet153. That is, the second adhesive layer 156 may be formed of at leastone of an acrylic-based polymer resin, a polyester-based polymer resin,or a polycarbonate-based polymer resin. The adhesive layer 157 mayinclude at least one diffusing agent of organic diffusing agent orinorganic diffusing agent to diffuse the light passing therethrough. Thesecond adhesive layer 156 may have a thickness of about 0.1 micrometersto about 5 micrometers.

The optical sheet 650 includes one base sheet 153 to collect the light,and thus the manufacturing cost for the optical sheet 650 may bereduced. The optical sheet 650 may prevent the base sheet 153 from beingcurled or wrinkled. In addition, the optical sheet 650 may prevent thesecond patterns 152 from being separated by using the second adhesivelayer 156, thereby enhancing the adhesive force between the secondpatterns 152.

FIG. 10 is a cross-sectional view showing an optical sheet according toa seventh exemplary embodiment.

Referring to FIG. 10, an optical sheet 750 includes a base sheet 153, aplurality of first patterns 154, a plurality of second patterns 152, asecond adhesive layer 156, and a protective layer 158. The secondadhesive layer 156 is disposed between the second patterns 152 toconnect ends of two adjacent second patterns 152. In detail, each of thesecond patterns 152 has the shape of the prism mountain, and the secondadhesive layer 156 covers an area at which a base vertex of the prismmountain meets a base vertex of the adjacent prism mountain, therebypreventing the second patterns 152 from being separated from each other.

The second adhesive layer 156 may include the same material as theadhesive layer 157 that fixes the second patterns 152 to the base sheet153. That is, the second adhesive layer 156 may be formed of at leastone of an acrylic-based polymer resin, a polyester-based polymer resin,or a polycarbonate-based polymer resin. The adhesive layer 157 mayinclude at least one diffusing agent of organic diffusing agent orinorganic diffusing agent to diffuse the light passing therethrough. Thesecond adhesive layer 156 may have a thickness of about 0.1 micrometersto about 5 micrometers.

The protective layer 158 is disposed below the lower surface of thesecond patterns 152 to prevent the second patterns 152 from beingseparated. The protective layer 158 may include the same material as theprotective layer 155 provided with the optical sheet 350 according tothe third exemplary embodiment, or as the second patterns 156.

The optical sheet 750 of FIG. 10 includes one base sheet 153 to collectthe light, and thus the manufacturing cost for the optical sheet 750 maybe reduced. The optical sheet 750 may prevent the base sheet 153 frombeing curled or wrinkled. In addition, since the optical sheet 750 mayprevent the second patterns 152 from being separated by using the secondadhesive layer 156 and the protective layer 158, the adhesive forcebetween the second patterns 152 may be enhanced.

FIG. 11 is a perspective view showing an optical sheet according to aneighth exemplary embodiment. FIG. 12 is a perspective view showing anoptical sheet according to a ninth exemplary embodiment.

Referring to FIG. 11, an optical sheet 850 includes second patterns 152,each having a triangular prism shape. Except for the triangular ratherthan trapezoidal shape of the second patterns 152, the optical sheet 850has the same structure and substantially same function as those of theoptical sheet 250 according to the second exemplary embodiment as shownin FIGS. 4 and 5.

The optical sheet 850 includes one base sheet 153 to collect the light,and thus the manufacturing cost for the optical sheet 850 may bereduced. The optical sheet 850 may prevent the base sheet 153 from beingcurled or wrinkled. In addition, since the optical sheet 850 has a moreperfect triangular prism shape approximation different from the shape ofthe optical sheet 250 as shown in FIGS. 4 and 5, the optical sheet 850may have a better light-collecting efficiency compared with that of theoptical sheet 250 shown in FIGS. 4 and 5. Further, the optical sheet 850may prevent the second patterns 152 from being separated by using theprotective layer 155, thereby enhancing the adhesive force between thesecond patterns 152.

Referring to FIG. 12, an optical sheet 950 includes second patterns 152,each having a triangular prism shape. Except for the shape of thetriangular second patterns 152, the optical sheet 950 has thesubstantially same structure and substantially same function as those ofthe optical sheet 550 according to the fifth exemplary embodiment asshown in FIG. 8.

The optical sheet 950 includes one base sheet 153 to collect the light,and thus the manufacturing cost for the optical sheet 950 may bereduced. The optical sheet 950 may prevent the base sheet 153 from beingcurled or wrinkled. In addition, since the optical sheet 950 has aperfect prism shape approximation different from the shape of theoptical sheet 550 as shown in FIG. 8, the optical sheet 950 may have thelight-collecting efficiency compared with the optical sheet 550 shown inFIG. 8. Further, the optical sheet 950 may prevent the second patterns152 from being separated by using the supporters 155-1 and 155-2,thereby enhancing the adhesive force between the second patterns 152.

FIGS. 13A to 13E are views showing a method of manufacturing an opticalsheet 150 according to a first exemplary embodiment of the presentdisclosure. Hereinafter, the manufacturing method of the optical sheet150 will be described in detail with reference to FIGS. 2, 3, and 13A to13E.

Referring to FIGS. 3 and 13A, before forming the second patterns 152, arelease layer 151P is formed on one surface of an auxiliary base sheet151 on which the second patterns 152 are thereafter formed. Theauxiliary base sheet 151 may be rigid and may function as an initial butremovable base on top of which subsequent layers are added. The releaselayer 151P may be formed by coating the one surface of the auxiliarybase sheet 151 with a selectively removable polymer resin.

Then, as shown in FIG. 13B, the trapezoidal second patterns 152 areformed on the release layer 151P using for example an extrusion moldingmethod or a soft molding method.

To this end, the polymer resin that is curable using UV radiation iscoated on the release layer 151P and the polymer resin is brought to thehalf-cured condition by irradiation with the UV light, thereby forming apartially-cured polymer resin layer. The polymer resin should not belimited to the UV curable material, that is, the polymer resin may be aheat curable material, where in the latter case, IR heat lamps may beused.

In the case that the second patterns 152 are formed using the extrusionmolding method, a master roll (not shown) is prepared to transfer thesecond patterns 152. The master roll is provided with reverse patternsformed a surface thereof to correspond to the topology of the top majorsurface of the second patterns 152. The master roll may be prepared in acylinder-shape roller. In case of using the extrusion molding method,the surface of the cylinder-shape roller is scratched along the axisdirection of the cylinder-shape roller by a grinder such as a diamondbite, so that a prism mountain pattern of which the top portion is cutaway may be formed on the surface of the cylinder-shape roller.

Then, the master roll is rotated while being pressed to make contactwith the auxiliary base sheet 151 on which the polymer resin layer isformed. When the master roll makes contact with the auxiliary base sheet151, the topology of the second patterns 152 is created in thepartially-cured polymer resin layer. Then, the polymer resin layer isfurther cured, thereby forming the second patterns 152 on the surface ofthe auxiliary base sheet 151.

In the case that the second patterns 152 being formed by using the softmolding method, a master mold (not shown) on which reverse patternscorresponding to required patterns are formed is prepared. Then, themaster mold on which the reverse patterns are formed is pressed to makecontact with the polymer resin layer. Accordingly, the reverse patternsare transferred to the polymer resin layer. Then, when the polymer resinlayer is more fully cured, the second patterns 152 may be formed on thesurface of the auxiliary base sheet 151.

After that, or in parallel therewith, the material of the first patterns154 are formed on the front surface 153F of the base sheet 153 as shownin FIG. 13C. Similar to the second patterns 152, the first patterns 154may be formed on the front surface 153F of the base sheet 153 using theextrusion molding method or the soft molding method. In detail, thepolymer resin that is curable using the UV radiation is coated on thefront surface 153F of the base sheet 153 and the polymer resin isbrought to a half-cured condition by irradiation of the UV light,thereby forming a polymer resin layer. Then, the cylinder-shape rolleron which the reverse patterns are formed corresponding to the firstpatterns 154 is pressed to make contact with the polymer resin layer onthe front surface 153F of the base sheet 153, or the master mode onwhich the reverse patterns are formed corresponding to the firstpatterns 154 is pressed to make contact with the polymer resin layer onthe front surface 153F of the base sheet 153, thereby transferring thereverse patterns to the polymer resin layer. Next, when the polymerresin layer is more fully-cured, the first patterns 154 may be formed onthe front surface 153F of the base sheet 153.

More specifically, and as shown in FIG. 13C, the adhesive layer 157 isthen formed on the rear surface 153R of the base sheet 153 on which thefirst patterns 154 are formed. The adhesive layer 157 may be formed bycoating a melted polymer resin or a half-cured polymer resin. The meltedpolymer resin is pre-cured until it is brought to the half-curedcondition, and the polymer resin may be an UV curable polymer resin. Inthe present exemplary embodiment, the adhesive layer 157 is formedentirely on the rear surface 153R of the base sheet 153, but it shouldnot be limited thereto. That is, the adhesive layer 157 may be formedpartially on the rear surface 153R of the base sheet.

Then, as shown in FIG. 13D, the second patterns 152 are press attachedto the rear surface 153R of the base sheet 153. In this case, theauxiliary base sheet 151 is pressed to the base sheet 153 such that theupper surface 152T of the first patterns 152 make substantially directcontact through the adhesive layer 157 with each other, and then thehalf-cured polymer resin is cured completely to thereby bond the layerstogether. Although not shown in FIGS. 13A to 13E, a portion of theadhesive layer 157 may remain between the upper surface 152T of thesecond patterns 152 and the rear surface 153R of the base sheet 153.

Referring to FIG. 13E, the auxiliary base sheet 151 disposed below thesecond patterns 152 is removed by using a solvent or other releasingagent to release the release layer. Thus, the optical sheet 150 shown inFIGS. 2 and 3 may be completely manufactured.

FIGS. 14A to 14E are views showing a method of manufacturing the opticalsheet 250 according to the second exemplary embodiment of the presentinvention. In FIGS. 14A to 14E, the same reference numerals denote thesame elements in FIGS. 13A to 13E, and thus detailed descriptions of thesame elements will be omitted.

Referring to FIG. 14A, the release layer 151P is formed on the auxiliarybase sheet 151. The processes of forming the release layer 151P are thesame as the processes of forming the release layer 151P shown in FIG.13A, so details thereof will be omitted.

Then, as shown in FIG. 14B, the protective layer 155 and the secondpatterns 152 are formed on the release layer 151P. In the presentexemplary embodiment, the protective layer 155 and the second patterns152 may be formed through the single process.

In order to form the second patterns 152 and the protective layer 155,the half-cured polymer resin or the melted polymer resin is coated onthe auxiliary base sheet 151. Then, the UV light or the heat is appliedto the polymer resin on the auxiliary base sheet 151 to form the polymerresin layer. The polymer resin layer has a thickness the same as the sumof the height H1 of the second patterns and the thickness H2 of theprotective layer 155.

After that, as described with reference to FIG. 13B, after the secondpatterns 152 are formed by using the extrusion molding method or thesoft molding method, the polymer resin layer is cured using the UV lightor the heat. In this case, the height of the reverse patterns formed onthe master roll or the master mold is the same as the height H1 of thesecond patterns 152. Accordingly, the second patterns 152 aretransferred to the polymer resin layer by the height H1 of the secondpatterns 152 from the upper surface of the polymer resin layer, and thesecond patterns 152 are not formed in other portion. Thus, theprotective layer 155 remains in the other portion in which the secondpatterns 152 are not formed.

Then, the first patterns 154 are formed on the base sheet 153 and theadhesive layer 157 is formed on the rear surface 153R of the base sheet153 as shown in FIG. 14C. As shown in FIG. 14D, the base sheet 153 iscoupled by press attachment with the auxiliary base sheet 151, and theadhesive layer 157 is more fully cured. Since the processes shown inFIGS. 14C and 14D are the same as the processes shown in FIGS. 13C and13D, details thereof will be omitted.

As shown in FIG. 14E, when the auxiliary base sheet 151 is removed(released away), the optical sheet 250 shown in FIGS. 4 and 5 ismanufactured.

In the present exemplary embodiment, the protective layer 155 is formedtogether with the second patterns 152, but it should not be limitedthereto. That is, the protective layer 155 may be formed by coating thepolymer resin on the rear surface 153R of the base sheet 153 afterremoving the auxiliary base sheet 151.

In addition, in the first and second exemplary embodiments, the opticalsheet 150 is manufactured by coupling the base sheet 153 with theauxiliary base sheet 151, on which the second patterns 152 are formed,after the first patterns 154 are formed on the base sheet 153. However,the first patterns 154 may be formed on the front surface 153F of thebase sheet 153 after coupling the base sheet 153 with the auxiliary basesheet 151 on which the second patterns 152 are formed before the firstpatterns 154 are formed.

Although the exemplary embodiments in accordance with the presentteachings have been described, it is understood that the presentdisclosure should not be limited to these exemplary embodiments butvarious changes and modifications can be made by one ordinary skilled inthe art in light of the foregoing and within the spirit and scope of thepresent teachings.

What is claimed is:
 1. An optical sheet comprising: a light-passing basesheet having a first surface and a second surface facing the firstsurface; a plurality of light-passing first patterns disposed on thefirst surface of the base sheet; a plurality of light-passing secondpatterns, each combined with the second surface of the base sheet; andan inner layer disposed between the plurality of light-passing secondpatterns and the light-passing base sheet and having a refractive indexgreater than refractive indices of plurality of light-passing secondpatterns.
 2. The optical sheet of claim 1, wherein each of the pluralityof light-passing second patterns comprises an upper surfacesubstantially parallel to the second surface of the base sheet and anlower surface substantially parallel to the upper surface and the lowersurface has a width longer than the upper surface in a first direction.3. The optical sheet of claim 2, further comprising a first adhesivelayer disposed on the second surface of the base sheet, wherein thefirst adhesive layer is contacted with the inner layer.
 4. The opticalsheet of claim 3, wherein a height is defined from the lower surface tothe first adhesive layer has a value of about 75% of a height of each ofthe plurality of light-passing second patterns.
 5. The optical sheet ofclaim 1, wherein each of the plurality of light-passing first patternshas a prismatic shape extending longitudinally in the first direction.6. The optical sheet of claim 5, wherein each of the plurality oflight-passing second patterns has a prismatic shape extendinglongitudinally in a second direction substantially perpendicular to thefirst direction.
 7. The optical sheet of claim 1, wherein each of theplurality of light-passing second patterns has a lower surface, and thelower surface of each of the plurality of light-passing second patternsis connected to the lower surface of adjacent second pattern through anend thereof.
 8. The optical sheet of claim 7, further comprising asecond adhesive layer disposed between two adjacent ones of theplurality of light-passing second patterns to thereby connect the endsof the two adjacent second patterns to each other.
 9. The optical sheetof claim 7, further comprising a protective layer disposed on the lowersurface of the plurality of light-passing second patterns.
 10. Theoptical sheet of claim 9, wherein the protective layer is integrallyformed with the plurality of light-passing second patterns and comprisesa same material as the plurality of light-passing second patterns. 11.The optical sheet of claim 9, wherein the protective layer has a firstprotective pattern and a second protective pattern being apart from thefirst protective pattern, the first protective pattern and the secondprotective pattern extend in the first direction.
 12. The optical sheetof claim 9, wherein the protective layer comprises a material differentfrom the base sheet.
 13. The optical sheet of claim 9, wherein theprotective layer has a thickness corresponding to a value of about 25%or more of the height of the plurality of light-passing second patterns,and the base sheet has a thickness larger than two times the height ofthe plurality of light-passing second patterns.
 14. The optical sheet ofclaim 1, wherein each of the plurality of light-passing first patternshas a lenticular shape extending longitudinally in the first direction.15. The optical sheet of claim 14, wherein each of the plurality oflight-passing second patterns has a lenticular shape extendinglongitudinally in a second direction substantially perpendicular to thefirst direction.
 16. A method of manufacturing an optical sheet,comprising: forming a plurality of light-passing second patterns on onesurface of an auxiliary base sheet to allow the plurality oflight-passing second patterns to protrude above the auxiliary basesheet; forming a plurality of light-passing first patterns on a frontsurface of a base sheet to allow the plurality of light-passing firstpatterns to protrude above the base sheet; forming a first adhesivelayer on a rear surface of the base sheet; coupling the plurality oflight-passing second patterns that are disposed on the auxiliary basesheet with the base sheet such that the plurality of light-passingsecond patterns make contact with the first adhesive layer, wherein aninner layer is defined between the plurality of light-passing secondpatterns and the base sheet and the inner layer has a refractive indexgreater than refractive indices of plurality of light-passing secondpatterns; and removing the auxiliary base sheet.
 17. The method of claim16, further comprising forming a release layer on the one surface of theauxiliary base sheet prior to forming the plurality of light-passingsecond patterns to attach or detach the plurality of light-passingsecond patterns.
 18. The method of claim 16, wherein the first adhesivelayer comprises an ultraviolet light curable resin.
 19. The method ofclaim 16, wherein the forming of the plurality of light-passing secondpatterns further comprises forming a protective layer between theauxiliary base sheet and the plurality of light-passing second patterns.20. The method of claim 19, wherein the second plurality oflight-passing patterns comprise a same material as the protective layer,the protective layer comprises a material different from the base sheet,and the second plurality of light-passing patterns and the protectivelayer are integrally formed through a single process.
 21. The method ofclaim 16, further comprising forming a second adhesive layer between twoadjacent second patterns to connect ends of the plurality oflight-passing second patterns to each other prior to coupling theauxiliary base sheet with the base sheet.
 22. The method of claim 16,further comprising forming a protective layer on the lower surface ofthe plurality of light-passing second patterns after removing theauxiliary base sheet.